WO2021111556A1

WO2021111556A1 - Light-emitting device

Info

Publication number: WO2021111556A1
Application number: PCT/JP2019/047493
Authority: WO
Inventors: 峻之中; 上田　吉裕; 岩田　昇
Original assignee: シャープ株式会社
Priority date: 2019-12-04
Filing date: 2019-12-04
Publication date: 2021-06-10
Also published as: US20230006166A1

Abstract

This light-emitting device (100) has an HTL (3) containing a metal chalcogenide between a positive electrode (2) and an EML (5), and has at least an IL (4) that includes an organic material between the HTL and the EML. The distance between the HTL and the EML in a light-emitting element (10B) that emits light of the shortest wavelength band among light-emitting peak wavelengths, is greater than the distance between the HTL and the EML in other light-emitting elements (10R, 10G).

Description

Luminescent device

This disclosure relates to a light emitting device.

In Non-Patent Document 1, blue quantum dots are used for the light emitting layer, and in a light emitting device using an organic material for the hole injection layer and the hole transport layer, the ligand of the blue quantum dots is replaced with a shorter ligand. It is disclosed that quantum efficiency can be improved.

Further, in Non-Patent Document 2, in a light emitting device in which green quantum dots are used for the light emitting layer and NiO (nickel oxide) is used for the hole transport layer, the thickness of the shell of the green quantum dots is increased. It is disclosed that light emission quenching and deterioration of device performance are suppressed.

As described above, in Non-Patent Document 1, the distance from the carrier transport layer to the quantum dot core is shortened in order to improve the characteristics of the light emitting device. On the other hand, in Non-Patent Document 2, contrary to Non-Patent Document 1, the distance from the carrier transport layer to the core of the quantum dot is increased in order to improve the characteristics of the light emitting element.

As described above, Non-Patent Document 1 uses a general organic material for the hole injection layer and the hole transport layer. On the other hand, Non-Patent Document 2 uses NiO for the hole transport layer as described above. NiO is a kind of metal chalcogenide (metal oxide, metal sulfide, etc.).

However, as a result of diligent studies by the inventors of the present application, the inventors of the present application have found the following problems. That is, in a light emitting device provided with light emitting elements having different emission wavelengths, when metal chalcogenide is used for the layer having hole transporting property and the thickness of the quantum dot shell in each light emitting element is increased, the emission peak wavelength is the shortest. The brightness of the light emitting element that emits light in the wavelength band becomes low.

Therefore, one aspect of the present disclosure includes a light emitting element that emits light in a wavelength band having the shortest emission peak wavelength in a light emitting device including a light emitting element having a layer containing a metal chalcogenide having a hole transporting property, and another light emitting element. The purpose is to balance the brightness with the light emitting element.

In order to solve the above problems, the light emitting element according to one aspect of the present disclosure includes a plurality of types of light emitting elements having emission peak wavelengths in different wavelength bands, and the plurality of types of light emitting elements are each provided with an anode. A light emitting layer containing quantum dots and a cathode are provided in this order, and a layer containing a metal chalcogenide having a hole transporting property is provided between the anode and the light emitting layer, and the plurality of types of light emitting elements are described above. Among the above-mentioned plurality of types, at least, in a light emitting element that emits light in the wavelength band having the shortest emission peak wavelength, an intermediate layer containing an organic material is provided between the layer containing the metal chalcogenide and the light emitting layer. Among the light emitting elements, the distance between the layer containing the metal chalcogenide and the light emitting layer in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is the metal chalcogenide in the other light emitting element. It is larger than the distance between the layer containing the above and the light emitting layer.

According to one aspect of the present disclosure, a light emitting element including a light emitting element having a layer containing a metal chalcogenide having a hole transporting property and emitting light in a wavelength band having the shortest emission peak wavelength, and another light emitting element. It is possible to provide a light emitting device capable of balancing brightness.

It is a figure which shows typically an example of the laminated structure of the light emitting device which concerns on Embodiment 1. FIG. It is sectional drawing which shows typically the schematic structure of the quantum dot and the ligand contained in each light emitting layer of the light emitting device which concerns on Embodiment 1. FIG. It is a figure which shows the energy band and the layer thickness of each layer in the red light emitting element which concerns on Embodiment 1. FIG. It is a figure which shows the energy band and the layer thickness of each layer in the green light emitting element which concerns on Embodiment 1. FIG. It is a figure which shows the energy band and the layer thickness of each layer in the blue light emitting element which concerns on Embodiment 1. FIG. It is sectional drawing which shows typically the schematic structure of the quantum dot and the ligand contained in each light emitting layer of the light emitting device which concerns on Embodiment 2. FIG. It is a figure which shows the energy band and the layer thickness of each layer in the red light emitting element which concerns on Embodiment 2. It is a figure which shows the energy band and the layer thickness of each layer in the green light emitting element which concerns on Embodiment 2. It is a figure which shows the energy band and the layer thickness of each layer in the blue light emitting element which concerns on Embodiment 2.

[Embodiment 1]
Hereinafter, an embodiment of the present disclosure will be described. In the following, the layer formed in the process before the layer to be compared is referred to as the “lower layer”, and the layer formed in the process after the layer to be compared is referred to as the “upper layer”.

FIG. 1 is a diagram schematically showing an example of a laminated structure of the light emitting device 100 according to the present embodiment.

As shown in FIG. 1, the light emitting device 100 includes an array substrate 1 as a support and a plurality of types of light emitting elements 10 having emission peak wavelengths in different wavelength bands. The light emitting device 100 has a structure in which each layer of the light emitting element 10 is laminated on an array substrate 1 on which a TFT (thin film transistor) (not shown) is formed. In the present disclosure, the direction from the array substrate 1 side toward the light emitting element 10 side is described as "upward", and the direction from the light emitting element 10 side toward the array substrate 1 side is described as "downward".

The light emitting device 100 is a display device (QLED display) provided as a light emitting element 10 with a quantum dot light emitting diode (hereinafter referred to as "QLED") using quantum dots (semiconductor nanoparticles) QD as a light emitting material. The light emitting device 100 includes a plurality of pixels P, and a light emitting element 10 is provided for each pixel P corresponding to the pixel P.

The light emitting element 10 includes an anode 2, a light emitting layer (hereinafter referred to as “EML”) 5, and a cathode 7 in this order. A hole transport layer (hereinafter referred to as "HTL") 3 is provided between the anode 2 and the EML 5 as a layer containing a metal chalcogenide having a hole transport property. Between HTL3 and EML5, an insulating layer (hereinafter, referred to as “IL”) 4 containing an organic material is provided as an intermediate layer between HTL3 and EML5. An electron transport layer (hereinafter referred to as "ETL") 6 may be provided between the EML 5 and the cathode 7 as a layer having electron transportability.

The light emitting element 10 shown in FIG. 1 includes an anode 2, HTL3, IL4, EML5, ETL6, and a cathode 7 in this order from the array substrate 1 side (that is, the lower layer side).

Each of the anode 2, HTL3, IL4, and EML5 is separated into islands for each pixel P by a bank (not shown). As a result, the light emitting device 100 is provided with a plurality of QLEDs as the light emitting element 10 corresponding to the pixel P.

The bank functions as a pixel separation wall and also functions as an edge cover that covers each edge of the

anodes

2R, 2G, and 2B. For the bank, for example, an insulating material such as an acrylic resin or a polyimide resin is used.

The light emitting device 100 shown in FIG. 1 has a red pixel RP, a green pixel GP, and a blue pixel BP as the pixel P. The pixel RP is provided with a light emitting element 10R (red light emitting element) that emits red light as the light emitting element 10. The green pixel GP is provided with a light emitting element 10G (green light emitting element) that emits green light as the light emitting element 10. The blue pixel BP is provided with a light emitting element 10B (blue light emitting element) that emits blue light as the light emitting element 10.

Hereinafter, the island-shaped anode 2 separated from each other corresponding to the pixel RP, the pixel GP, and the pixel BP by the above bank will be referred to as an anode 2R, an anode 2G, and an anode 2B, respectively. Similarly, the island-shaped HTL3s separated from each other corresponding to the pixel RP, the pixel GP, and the pixel BP by the above bank are referred to as HTL3R, HTL3G, and HTL3B, respectively. The island-shaped IL4s separated from each other corresponding to the pixel RP, the pixel GP, and the pixel BP by the above bank are referred to as IL4R, IL4G, and IL4B in this order. The island-shaped EML5s separated from each other corresponding to the pixel RP, the pixel GP, and the pixel BP by the above bank are referred to as EML5R, EML5G, and EML5B, respectively. The ETL 6 and the cathode 7 are not separated by the bank, and are formed as a common layer in a solid shape in the display region in common with all the pixels P.

The light emitting element 10R is formed by island-shaped anodes 2R, HTL3R, IL4R, EML5R, and common layers ETL6 and cathode 7, respectively. The light emitting element 10G is formed by island-shaped anodes 2G, HTL3G, IL4G, EML5G, and common layers ETL6 and cathode 7, respectively. The light emitting element 10B is formed by an island-shaped anode 2B, HTL3B, IL4B, EML5B, and common layers ETL6 and cathode 7, respectively.

The

anodes

2R, 2G, and 2B, which are the lower electrodes formed on the array substrate 1, are pattern anodes provided for each pixel P, and are electrically connected to the TFT of the array substrate 1, respectively. On the other hand, the cathode 7, which is the upper electrode, is a common cathode common to all pixels P.

The layers of the

light emitting elements

10R, 10G, and 10B are the layers corresponding to each other in the

light emitting elements

10R, 10G, and 10B, except for EML5R, 5G, and 5B, and may be formed of the same material.

The EML5R has a quantum dot QR that emits red light as a quantum dot QR. The EML5G includes a quantum dot QG that emits green light as a quantum dot QD. The EML5B includes a quantum dot QB that emits blue light as a quantum dot QD.

In the present disclosure, red light refers to light having an emission peak wavelength in a wavelength band of 600 nm or more and 780 nm or less. Further, green light refers to light having an emission peak wavelength in a wavelength band of 500 nm or more and 600 nm or less. Blue light refers to light having an emission peak wavelength in a wavelength band of 400 nm or more and 500 nm or less.

The light emitting element 10R preferably has a light emitting peak wavelength in a wavelength band of 620 nm or more and 650 nm or less. The light emitting element 10G preferably has an emission peak wavelength in a wavelength band of 520 nm or more and 540 nm or less. The light emitting element 10B preferably has an emission peak wavelength in a wavelength band of 440 nm or more and 460 nm or less.

However, the above configuration is an example, and the configuration of the light emitting device 100 is not necessarily limited to the above configuration. The light emitting device 100 may include, as the light emitting element 10, a light emitting element that emits light having a light emitting peak wavelength in a wavelength band other than the above wavelength band. The ETL6 may be separated into islands for each pixel P by the bank. The stacking order from the anode 2 to the cathode 7 may be reversed. Therefore, the light emitting element 10 may include the anode 2, HTL3, IL4, EML5, ETL6, and cathode 7 in this order from the upper layer side. When the cathode 7 is a lower electrode formed on the array substrate 1, the cathode 7 is electrically connected to the TFT of the array substrate 1 as a pattern cathode. On the other hand, the anode 2 serving as the upper electrode is used as a common anode common to all pixels P. Hereinafter, a case where the light emitting device 100 has the configuration shown in FIG. 1 will be described as an example.

In the following description, when it is not necessary to distinguish the

light emitting elements

10R, 10G, and 10B, as described above, these

light emitting elements

10R, 10G, and 10B are collectively referred to simply as "light emitting element 10." Similarly, when it is not necessary to distinguish between the pixel RP, GP, and BP, these pixel RP, GP, and BP are collectively referred to simply as "pixel P". When it is not necessary to distinguish between the

anodes

2R, 2G and 2B, these

anodes

2R, 2G and 2B are collectively referred to simply as "anode 2". When it is not necessary to distinguish between HTL3R, 3G, and 3B, these HTL3R, 3G, and 3B are collectively referred to simply as "HTL3". When it is not necessary to distinguish IL4R, 4G, and 4B, these IL4R, 4G, and 4B are collectively referred to as "IL4". When it is not necessary to distinguish between EML5R, 5G and 5B, these EML5R, 5G and 5B are collectively referred to as "EML5". When it is not necessary to distinguish between the quantum dots QR, QG, and QB, these quantum dots QR, QG, and QB are collectively referred to simply as "quantum dot QD".

The anode 2 is made of a conductive material and has a function of a hole injection layer (hereinafter referred to as "HIL") for injecting holes into HTL3. The cathode 7 is made of a conductive material and has a function of an electron injection layer (hereinafter referred to as “EIL”) for injecting electrons into the ETL6.

Either the anode 2 or the cathode 7 is made of a light-transmitting material. Either one of the anode 2 and the cathode 7 may be made of a light-reflecting material. When the light emitting device 100 is a top emission type light emitting device, the upper layer cathode 7 is formed of a light transmitting material, and the lower layer anode 2 is formed of a light reflecting material. When the light emitting device 100 is a bottom emission type light emitting device, the cathode 7 which is the upper layer is formed of a light reflecting material, and the anode 2 which is a lower layer is formed of a light transmitting material.

As the light transmissive material, for example, a transparent conductive material can be used. Specifically, as the light-transmitting material, for example, ITO (indium tin oxide), IZO (indium zinc oxide), SnO ₂ (tin oxide), FTO (fluorine-doped tin oxide) and the like can be used. .. Since these materials have high visible light transmittance, the luminous efficiency is improved.

As the light-reflecting material, for example, a metal material can be used. Specifically, as the light-reflecting material, for example, Al (aluminum), Ag (silver), Cu (copper), Au (gold) and the like can be used. Since these materials have high visible light reflectance, the luminous efficiency is improved.

Further, one of the anode 2 and the cathode 7 may be a light-reflecting electrode by forming a laminate of a light-transmitting material and a light-reflecting material.

The anode 2 and the cathode 7 can be formed by various conventionally known methods for forming the anode 2 and the cathode 7, such as a sputtering method and a vacuum deposition method.

ETL6 transports electrons to EML5. The ETL6 may have a function of inhibiting the transport of holes. The ETL 6 may also serve as an EIL that promotes the injection of electrons from the cathode 7 into the EML 5. When a layer having electron transportability is provided between the cathode 7 and the EML 5, the light emitting element 10 may be provided with EIL and ETL6 in this order from the cathode 7 side, or may be provided with only ETL6.

A known electron transporting material can be used for ETL6. As the electron transporting material, for example, zinc oxide (for example, ZnO), titanium oxide (for example, TiO ₂ ), strontium oxide titanium (for example, SrTiO ₃ ) and the like are used. Only one kind of these electron transporting materials may be used, or two or more kinds may be mixed and used as appropriate. Further, nanoparticles may be used as the electron transporting material.

HTL3 transports holes to EML5 via IL4. In addition, HTL3 may have a function of inhibiting the transport of electrons. In addition, HTL3 may also serve as HIL that promotes the injection of holes from the anode 2 into the EML5.

As described above, HTL3 is a layer containing a metal chalcogenide having a hole transporting property. Although HTL3 mainly contains metallic chalcogenide, it may further contain other materials. Metallic chalcogenide is particularly durable among inorganic materials. Metal chalcogenides, for example, nickel oxide (eg NiO), copper oxide (e.g., _Cu 2 O), include copper sulfide (e.g., CuS), and the like. Only one kind of these metal chalcogenides may be used, or two or more kinds may be mixed and used as appropriate. Therefore, the metal chalcogenide may be at least one selected from the group consisting of nickel oxide, copper oxide, and copper sulfide.

HTL3 can be formed by, for example, a sol-gel method, a sputtering method, a CVD (chemical vapor deposition) method, a spin coating method (coating method), or the like.

IL4 is provided between HTL3 and EML5 in contact with HTL3 and EML5. Although IL4 mainly contains an organic material, it may further contain other materials.

IL4 is formed by using an insulating material that can be uniformly laminated without any trouble such as disappearance due to dissolution of the lower layer or repelling when the material is applied to the lower layer in the manufacturing process. As the insulating material, an organic material that is not a good conductor is desirable, and an organic material that does not have a hydroxyl group is more desirable. Further, in order to suppress the overflow of electrons from EML5 to HTL3, the electron affinity value of IL4 is preferably 0.5 eV or more smaller than the electron affinity value of EML5. Further, it is desirable that the value of the ionization potential of IL4 is larger than the value of the value of the ionization potential of EML5 minus 0.5 eV because it facilitates the injection of holes from HTL3 to EML5.

That is, the electron affinity of IL4 and _{EA IL,} when the electron affinity of EML5 with _{EA EML,} it is preferable that _{_EA IL} ≦ _EA EML _-0.5eV. Further, the _{IP IL} ionization potential of IL4, when the ionization potential of EML5 the _{IP EML,} it is preferable that the _{_IP IL} ≧ _IP EML _-0.5eV.

Examples of such an insulating material include polymethylmethacrylate (abbreviation: PMMA), polyvinylpyrrolidone (abbreviation: PVP), and poly [(9,9-bis (3'-(N, N-dimethylamino) propyl))-. 2,7-Fluorene) -alt-2,7- (9,9-dioctylfluorene)] (abbreviation: PFN) and the like can be mentioned. Only one kind of these insulating materials may be used, or two or more kinds may be mixed and used as appropriate. Therefore, IL4 may consist of at least one insulating material selected from the group consisting of PMMA, PVP, PFN.

As an example, the electron affinity, ionization potential, and band gap of these PMMA, PVP, and PFN are shown in Table 1. The bandgap corresponds to the difference between the ionization potential of the layer and the electron affinity.

IL4 can be formed by, for example, a spin coating method (coating method), a dip coating method, an inkjet method, or the like.

As mentioned above, metal chalcogenide has durability. Further, as described above, a light emitting device using quantum dot QD for EML is different from a light emitting device using organic EL for EML, and can be manufactured at low cost by a manufacturing process that does not use a high vacuum device. However, if a light emitting device using quantum dot QD as described above is manufactured by a manufacturing process using metal chalcogenide for HTL and without using a high vacuum device, the surface of the metal chalcogenide may be exposed by a gas containing water. is there. When the surface of the metal chalcogenide is exposed to even a small amount of a gas containing water, it is assumed that hydroxyl groups are adsorbed on the surface of the metal chalcogenide.

In particular, from the viewpoint of versatility of the manufacturing apparatus, it is desirable that the manufacturing apparatus of each layer of the light emitting element 10 is separated from each other. Therefore, it is desirable that the HTL3 manufacturing apparatus and the film forming apparatus used in the next step (that is, the film forming apparatus on the HTL3) are separated from each other. However, when the substrate on which the HTL3 is formed is conveyed to the manufacturing apparatus separated from the apparatus for producing the HTL3 after the formation of the HTL3, the substrate on which the HTL3 is formed is exposed to the atmosphere between the two manufacturing apparatus.

As described above, from the viewpoint of versatility of the manufacturing apparatus, the manufacturing process of the light emitting device 100 includes a step of exposing the metal chalcogenide surface of HTL3 to a gas containing water, but each layer in the light emitting element 10 It is desirable that the manufacturing equipment is separated from each other. Then, in the step of exposing the surface of the metal chalcogenide of HTL3 to a gas containing water, it is assumed that a hydroxyl group is adsorbed on the surface of the metal chalcogenide. Therefore, the fact that the manufacturing process of the light emitting device 100 includes a step of exposing the metal chalcogenide surface of HTL3 to a gas containing water includes a step of adsorbing a hydroxyl group on the surface of the metal chalcogenide. It is presumed to mean that.

IL4 suppresses the charging of the quantum dot QD by the hydroxyl group on the surface of the metal chalcogenide, and suppresses the deterioration of the light emission characteristic due to the charging of the quantum dot QD.

In addition, IL4 has the effect of controlling the transport of holes from HTL3 to EML5 and inhibiting the transport of electrons injected from the cathode 7. Therefore, the recombination efficiency of holes and electrons in EML5 can be increased, and the luminous efficiency can be improved.

EML5 is a layer containing a light emitting material and emitting light by recombination of electrons transported from the cathode 7 and holes transported from the anode 2. The light emitting device 100 includes quantum dot QDs in which a plurality of layers are laminated as a light emitting material in each pixel P.

The method for forming EML5 is not particularly limited, but for example, a solution method is preferably used instead of crystal growth or the like. In EML5, a dispersion liquid in which quantum dot QD is dispersed in a solvent (dispersion medium) is applied to the upper surface of a layer to be a lower layer of EML5 to form a coating film containing quantum dot QD, and then the solvent is volatilized. It can be formed by solidifying (curing) the coating film. As the solvent, water; an organic solvent such as hexane or toluene; can be used. The dispersion liquid is separately applied to each pixel P by using a spin coating method, an inkjet method, or the like. A dispersion material such as thiol or amine may be mixed with the dispersion liquid.

The dispersion liquid is a colloidal solution containing a quantum dot QD, a ligand that adsorbs (coordinates) the quantum dot QD on the surface of the quantum dot QD as a receptor, and the solvent. The ligand is a surface modifying group that modifies the surface of the quantum dot QD. The surface of the quantum dot QD is protected by a ligand.

The EML5 thus formed by the solution method contains a spherical quantum dot QD and a ligand. The coated quantum dot QD formed by the solution method in this way has a spherical shape rather than an island shape (lens shape) as in the case of crystal growth, thereby reducing the polarization characteristics of light emission. be able to. Further, since the EML5 contains a ligand, it is possible to suppress the aggregation of the quantum dot QD and satisfactorily disperse the quantum dot QD at the time of forming the coating film containing the quantum dot QD.

The light emitting device 100 includes a plurality of types of quantum dot QDs, and the same pixel P includes the same types of quantum dot QDs. The EML5R has, for example, a configuration in which a plurality of layers of quantum dot QR are laminated. The EML5G has, for example, a configuration in which a plurality of layers of quantum dot QGs are laminated. The EML5B has, for example, a configuration in which a plurality of layers of quantum dots QB are laminated.

FIG. 2 is a cross-sectional view schematically showing a schematic configuration of quantum dots QR / QG / QB and ligands LR / LG / LB contained in EML5R / 5G / 5B of the light emitting device 100.

The quantum dots QR, QG, and QB as the receptacles used in the present embodiment are core-shell type quantum dots (core-shell particles), and each of them has a core and a shell covering the core. (Core shell particles).

As shown in FIG. 2, the quantum dot QR includes a core CR and a shell SR that covers the core CR. Similarly, the quantum dot QG includes a core CG and a shell SG that covers the core CG. The quantum dot QB includes a core CB and a shell SB that covers the core CB.

Further, EML5R has a ligand LR adsorbed on the surface of the quantum dot QR. EML5G has a ligand LG adsorbed on the surface of the quantum dot QG. EML5B has a ligand LB adsorbed on the surface of the quantum dot QB.

Quantum dots QR / QG / QB are, for example, Cd (cadmium), S (sulfur), Te (tellurium), Se (selenium), Zn (zinc), In (indium), N (nitrogen), P (phosphorus). , As (arsenic), Sb (antimony), aluminum (Al), Ga (gallium), Pb (lead), Si (silicon), Ge (germanium), Mg (magnesium), at least one selected from the group. It may contain at least one kind of semiconductor material composed of the above elements.

For example, ZnS (zinc sulfide) is used for the shell SR / SG / SB. As the material of the shell SR / SG / SB, a material having a lattice constant similar to that of the core CR / CG / CB covered by the shell SR / SG / SB is preferably used. When the lattice constants of the core CR / CG / CB and the lattice constants of the shell SR / SG / SB covering the core CR / CG / CB are compatible, the amount of defects in the crystal can be reduced. .. Further, as the material of the shell SR / SG / SB, it is desirable to use a shell material having a band gap larger than that of the material of the core CR / CG / CB covered by the shell SR / SG / SB. By using such a material, PLQY (photoluminescence quantum yield) can be increased and the excited state can be protected. ZnS meets these requirements. However, the material of the shell SR / SG / SB is not limited to ZnS, and other suitable materials may be used.

The combination (core / shell) of the core CR / CG / CB and the shell SR / SG / SB in each quantum dot QR / QG / QB includes, for example, CdSe (cadmium selenide) / ZnSe (zinc selenide), CdSe. / ZnS, CdS (cadmium sulfide) / ZnSe, CdS / ZnS, ZnSe / ZnS, InP (indium phosphate) / ZnS, ZnO (zinc oxide) / MgO (magnesium oxide) and the like can be mentioned.

The ligands LR, LG, and LB are composed of an adsorbing group that adsorbs (coordinates) to the surface of each quantum dot QR, QG, and QB, and an alkyl group that binds to the adsorbing group. Examples of the adsorbing group include an amino group, a phosphine group, a carboxyl group, a hydroxyl group, a thiol group and the like. Moreover, as the above-mentioned alkyl group, an alkyl group having 2 to 50 carbon atoms can be mentioned.

Examples of the ligands LR, LG, and LB include hexadecylamine, oleylamine, octylamine, hexadecanethiol, dodecanethiol, trioctylphosphine, trioctylphosphine oxide, myristic acid, and oleic acid. The ligands LR, LG, and LB also have a role as a dispersant for improving the dispersibility of the quantum dots QR, QG, and QB in the dispersion liquid.

As a feature of the core-shell type quantum dot QD, the wavelength of light emitted by the core-shell type quantum dot QD depends on the particle size of the core, which is the light emitting part, and does not depend on the particle size of the shell. The wavelength of light emitted by the quantum dots QR, QG, and QB can be controlled by the particle sizes of the cores CR, CG, and CB of each quantum dot QR, QG, and QB.

In quantum dot QD, when the particle size of the core, which is the light emitting part, is increased, the emission wavelength tends to be longer, and when the particle size of the core is decreased, the emission wavelength tends to be shorter.

As shown in FIG. 2, assuming that the particle size (diameter size) of the core CR is d1, the particle size (diameter size) of the core CG is d11, and the particle size (diameter size) of the core CB is d21, then d1> d11> It is d21. The particle sizes of these cores CR, CG, and CB (hereinafter referred to as "core diameters") d1, d11, and d21 can be appropriately set so that a desired emission wavelength can be obtained depending on the material of the core CR, CG, and CB. Well, it is not particularly limited. These core diameters d1, d11, and d21 can be set in the same manner as in the conventional case.

The core diameters d1, d11, and d21 are, for example, 1 to 10 nm. The quantum dots QR, QG, and QB emit light having a wavelength corresponding to the band gap (prohibited band width) and the quantum level (excitation level). As described above, the quantum dots QR, QG, and QB according to the present embodiment are spherical and have a substantially uniform particle size. The quantum dots QR, QG, and QB emit light having wavelengths corresponding to the core diameters d1, d11, and d21 of the respective cores CR, CG, and CB, which are light emitting units.

Further, the outermost particle size of the quantum dot QR including the shell SR is d3, the outermost particle size of the quantum dot QG including the shell SG is d13, and the outermost particle size of the quantum dot QB including the shell SB is set. Assuming d23, these outermost particle sizes d3, d13, and d23 are, for example, 2 to 20 nm. The layer thickness of EML5R / 5G / 5B is preferably about several times the outermost particle sizes d3 / d13 / d23 of each quantum dot QR / QG / QB, and each quantum dot QR / QG in EML5R / 5G / 5B. -The number of overlapping layers of QB is, for example, 1 to 9 layers.

The core diameters d1, d11, and d21 can be calculated from the quantum size effect by analyzing the materials of the cores CR, CG, and CB. Further, the outermost particle diameters d13, d13, and d23 can be measured from a TEM (transmission electron microscope) image of a cross section of EML5R, 5G, and 5B. The thickness of the shell SR / SG / SB and the length of the ligands LR / LG / LB will be described later.

In the light emitting elements 10R / 10G / 10B according to the present embodiment, the layer thickness of the layers other than IL4R / 4G / 4B can be set in the same manner as the conventional light emitting element.

Table 2 shows the layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B according to the present embodiment. In Table 2, the layer thickness in parentheses indicates a suitable range of the layer thickness of each layer. The layer thickness outside the parentheses is a specific layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B used in the present embodiment, and is an example of a combination of layer thicknesses of each layer in the

light emitting elements

10R, 10G, and 10B. Shown.

As shown in Table 2, the layer thickness of the

anodes

2R, 2G, and 2B is preferably 20 nm to 200 nm. The layer thickness of HTL3R / 3G / 3B is preferably 20 nm to 150 nm. The IL4R layer thickness and the IL4G layer thickness are preferably 12 nm or less. The layer thickness of IL4B is preferably 0.5 to 12.5 nm. However, IL4R, 4G, and 4B are set so that the layer thickness of IL4B> the layer thickness of IL4R and the layer thickness of IL4B> the layer thickness of IL4G. The layer thickness of EML5R / 5G / 5B is preferably 15 nm to 80 nm. The layer thickness of ETL6 is preferably 20 nm to 150 nm. The layer thickness of the cathode 7 is preferably 50 nm to 200 nm.

Hereinafter, an example of a method for manufacturing the

light emitting elements

10R, 10G, 10B and the light emitting device 100 according to the present embodiment will be described with reference to FIGS. 1 and 2.

In the present embodiment, first, an array substrate 1 as a support is prepared, and an ITO layer having a layer thickness of 100 nm as

anodes

2R, 2G, and 2B is formed in a matrix by a sputtering method on the array substrate 1. (Anode forming step).

Next, a grid-like bank (not shown) was formed as a pixel separation wall and edge cover so as to cover each edge of the

anode

2R, 2G, and 2B (bank forming step).

Next, NiO was spin-coated on the

anodes

2R, 2G, and 2B, and then heated in the air to form a NiO layer having a layer thickness of 50 nm as HTL3R, 3G, and 3B (HTL forming step).

Next, a PMMA layer was formed on HTL3R / 3G / 3B as IL4R / 4G / 4B by a spin coating method using a solution of PMMA dissolved in acetone (IL formation step). The part other than the target of film formation is formed by using a mask, and the layer thickness of IL4R / 4G / 4B is adjusted by changing the concentration of PMMA in the above solution, the rotation speed at the time of spin coating, and the like. Was done. As a result, a PMMA layer having a layer thickness of 8 nm was formed as IL4B, and a PMMA layer having a layer thickness of 6 nm was formed as IL4R and IL4G, respectively.

Next, quantum dot QD layers having a layer thickness of 40 nm were formed on IL4R / 4G / 4B as EML5R / 5G / 5B by a spin coating method (EML forming step).

Next, a ZnO layer having a layer thickness of 50 nm, which is made of ZnO-NP (nanoparticles) as ETL6 so as to cover the EML5R, 5G, 5B and the above bank, is subjected to a spin coating method to form a common layer common to each pixel P. (ETL forming step). According to the present embodiment, the ETL6 is obtained by forming the ETL6 in at least a part of the

light emitting elements

10R, 10G, and 10B using the same electron transporting material as described above. It can be a common layer in the light emitting element of. According to the present embodiment, as described above, the ETL6 can be formed more easily by sharing the material of the ETL6 with the

light emitting elements

10R, 10G, and 10B.

Next, on the ETL6, an Al layer having a layer thickness of 100 nm was formed as a cathode 7 as a common layer common to each pixel P by a vacuum deposition method (cathode forming step).

As a result, the

light emitting elements

10R, 10G, and 10B according to the present embodiment were manufactured. The light emitting device 100 according to the present embodiment is manufactured by sealing the

light emitting elements

10R, 10G, and 10B with a sealing layer (not shown) after the cathode forming step.

Next, the effect of the light emitting device 100 according to the present embodiment will be described.

As a result of diligent studies on this reason, the inventors of the present application came to the following conclusions. As described above, Non-Patent Document 1 uses a general organic material for the hole injection layer and the hole transport layer. In such a light emitting element, the distance from the carrier transport layer to the core of the quantum dot is shortened because the blue quantum dot has a carrier from the carrier transport layer to the core of the quantum dot as compared with the red quantum dot and the green quantum dot. It is presumed that this is because it is difficult to inject.

On the other hand, Non-Patent Document 2 uses NiO for the hole transport layer as described above. NiO is a type of metallic chalcogenide. In such a light emitting device, the distance from the carrier transport layer to the core of the quantum dot is increased because the presence of hydroxyl groups on the surface of the metal chalcogenide causes the quantum dots to be charged and the characteristics of the light emitting device to deteriorate. It is estimated to be.

However, according to the study by the inventors of the present application, as described above, when metal chalcogenide is used for the layer having hole transporting property and the thickness of the quantum dot shell of each light emitting element having a different emission wavelength is increased, the thickness of the shell is increased. The brightness of the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength becomes low.

Therefore, the inventors of the present application repeated diligent studies. As a result, the inventors of the present application set the thickness of the intermediate layer between the layer made of the metal chalcogenide of the light emitting device that emits light in the wavelength band having the shortest emission peak wavelength and the EML to correspond to the thickness of the other light emitting device. It has been found that the above problems can be solved by making the thickness larger than that of the intermediate layer. Therefore, in the present embodiment, as described above, the layer thicknesses of ILR, 4G, and 4B are set so that the layer thickness of IL4B> the layer thickness of IL4R and the layer thickness of IL4B> the layer thickness of IL4G. ing. The reason for this will be described in more detail below with reference to FIGS. 2 to 5.

3 to 5 are diagrams showing the energy band and layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B according to the present embodiment, which are manufactured by the above-mentioned method. FIG. 3 shows the energy band and layer thickness of each layer in the light emitting element 10R. FIG. 4 shows the energy band and layer thickness of each layer in the light emitting element 10G. FIG. 5 shows the energy band and layer thickness of each layer in the light emitting element 10B.

As shown in FIGS. 3 to 5, the ITO layer as an anode 2R · 2G · 2B Fermi level (hereinafter, referred to as _{"E F1")} is 4.7 eV, the Fermi level of the Al layer as a cathode 7 The rank (hereinafter referred to as " _EF2 ") is 4.3 eV. The electron affinity of the NiO layer as HTL3R / 3G / 3B (hereinafter referred to as "EA _HTL ") is 1.9 eV, and the ionization potential (hereinafter referred to as "IP _HTL ") is 5.4 eV. The electron affinity of the ZnO layer as ETL6 (hereinafter referred to as "EA _ETL ") is 4.0 eV, and the ionization potential (hereinafter referred to as "IP _ETL ") is 7.5 eV. The electron affinity of the quantum dot QD layer as EML5R (hereinafter referred to as "EA _EMLR ") is 5.9 eV, and the ionization potential IP _EML (hereinafter referred to as "IP _EMLR ") is 3.9 eV. The electron affinity of the quantum dot QD layer as EML5G (hereinafter referred to as "EA _EMLG ") is 5.9 eV, and the ionization potential (hereinafter referred to as "IP _EMLG ") is 3.2 eV. The electron affinity of the quantum dot QD layer as EML5R / 5G / 5B (hereinafter referred to as "EA _EMLB ") is 5.9 eV, and the ionization potential (hereinafter referred to as "IP _EMLB ") is 3.2 eV. _{The electron affinity EA IL} of PMMA as IL4R / 4G / 4B is 2.6 eV as shown in Table 1, and the ionization potential IP _IL is 5.8 eV.

The electron affinity EA _HTL corresponds to the energy difference between the vacuum level (not shown) and the CBM (lower end of the conduction band) of HTL3R / 3G / 3B. The ionization potential IP _HTL corresponds to the energy difference between the vacuum level and the VBM (upper end of the valence band) of HTL3R / 3G / 3B. The electron affinity EA _IL corresponds to the energy difference between the vacuum level and the CBM of IL4R / 4G / 4B. The ionization potential IP _IL corresponds to the energy difference between the vacuum level and the VBM of IL4R / 4G / 4B. The electron affinity EA _EMLR corresponds to the energy difference between the vacuum level and the CBM of EML5R. The ionization potential IP _EMLR corresponds to the energy difference between the vacuum level and the VBM of EML5R. The electron affinity EA _EMLG corresponds to the energy difference between the vacuum level and the CBM of EML5G. The ionization potential IP _EMLG corresponds to the energy difference between the vacuum level and the VBM of EML5G. The electron affinity EA _EMLB corresponds to the energy difference between the vacuum level and the CBM of EML5B. The ionization potential IP _EMLB corresponds to the energy difference between the vacuum level and the VBM of EML5B. The electron affinity EA _ETL corresponds to the energy difference between the vacuum level and the CBM of the ETL6R. The ionization potential IP _ETL corresponds to the energy difference between the vacuum level and the VBM of ETL6R / 6G / 6B.

As shown in FIGS. 3 to 5, when a potential difference is applied between the cathode 7 and the

anodes

2R, 2G, and 2B in the light emitting device 100, electrons are emitted from the cathode 7 and holes are generated from the

anodes

2R, 2G, and 2B. Is injected toward EML5R, 5G, and 5B, respectively. As shown by e- in FIGS. 3 to 5, the electrons from the cathode 7 reach EML5R, 5G, and 5B via ETL6. On the other hand, as shown by h + in FIGS. 3 to 5, holes from the

anodes

2R, 2G, and 2B reach EML5R, 5G, and 5B via HTL3R, 3G, and 3B and IL4R, 4G, and 4B. The holes and electrons that have reached EML5R, 5G, and 5B are recombined at the quantum dots QR, QG, and QB in the respective pixels PR, PG, and PB, and emit light. The light emitted from the quantum dots QR, QG, and QB is reflected by, for example, the cathode 7 which is a metal electrode, passes through the

anodes

2R, 2G, and 2B which are transparent electrodes, and is radiated to the outside of the light emitting device 100.

In the light emitting elements 10R / 10G / 10B, when the layer thickness of IL4R / 4G / 4B is sufficiently thin, the holes conduct IL4R / 4G / 4B by tunneling.

The hole injection barrier from HTL3R to EML5R is indicated by the energy difference (IP _EMLR- IP _HTL _{) between the ionization potential IP EMLR} of EML5R and the ionization potential IP _{HTL of HTL3R.} Similarly, the hole injection barrier from HTL3G to _EML5G is indicated by the energy difference (IP _EMLG- IP _HTL ) between the ionization potential IP EMLG of EML5G and the ionization potential IP _{HTL of HTL3G.} The hole injection barrier from HTL3B to _EML5B is indicated by the energy difference (IP _EMLB- IP _HTL ) between the ionization potential IP EMLB of EML5B and the ionization potential IP _{HTL of HTL3B.}

As shown in FIGS. 3 to 5, in general, the VBM of the quantum dot QD layer does not change depending on the emission wavelength of the quantum dot QD used as the quantum dot QR / QG / QB in the case of the same material system. Therefore, in the case of the same material system, the ionization potentials IP _EMLR , IP _EMLG, and IP _EMLB are substantially the same. The reason for this is as follows. As for the quantum dots QR, QG, and QB, the smaller the atomic numbers of the elements constituting the core CR, CG, and CB of these quantum dots QR, QG, and QB, the smaller the number of closed shell orbitals, and the more difficult it is for the nuclei to be shielded by the closed shell orbitals. Therefore, the valence electrons of the quantum dots QR, QG, and QB are easily affected by the electric field created by the atomic nucleus, and tend to stay at a certain energy level.

Therefore, in the case of the same material system, the VBM of the quantum dot QD layer has substantially the same ionization potential, and the hole injection efficiency into the quantum dot QD layer does not depend on the emission wavelength. In particular, in the examples shown in FIGS. 3 to 5, the hole injection barrier from HTL3R / 3G / 3B to EML5R / 5G / 5B is as small as 0.5 eV or less, and from HTL3R / 3G / 3B to EML5R / 5G / 5B. High efficiency of hole injection into.

However, as shown in FIGS. 3 to 5, in general, the CBM of the quantum dot QD layer differs depending on the emission wavelength. In particular, in the case of the same material system, the energy level of the conduction band level of the quantum dot QD used as the quantum dot QR / QG / QB becomes deeper as the emission wavelength of the quantum dot QD is longer, and the emission wavelength of the quantum dot QD. The shorter the value, the shallower the energy level. This is because the conduction band level is deeper in the quantum dot QD having a small bandgap.

Therefore, among the light emitting elements 10R / 10G / 10B, the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength has a larger electron injection barrier than the other light emitting elements 10R / 10G.

The electron injection barrier from ETL6 to EML5R is indicated by the energy difference (EA _ETL- _{EA EMLR} _{) between the electron affinity EA ETL} of ETL6 and the electron affinity EA _{EMLR of EML5R.} The electron injection barrier from ETL6 to _EML5G is indicated by the energy difference (EA _ETL- _{EA EMLG) between the electron affinity EA ETL} of ETL6 and the electron affinity EA _{EMLG of EML5G.} The electron injection barrier from ETL6 to _EML5B is indicated by the energy difference (EA _ETL- _{EA EMLB) between the electron affinity EA ETL} of ETL6 and the electron affinity EA _{EMLB of EML5B.}

In the examples shown in FIGS. 3 to 5, the electron injection barriers from ETL6 to EML5R, EML5G, and EML5B are, respectively, 0.1 eV, 0.5 eV, and 0.8 eV, and the electron injection is R → G →. It becomes more difficult in the order of B. In particular, in the examples shown in FIGS. 3 to 5, the electron injection barrier from ETL6 to EML5R and EML5G is as small as 0.5 eV or less, and the electron injection transport from ETL6 to EML5R / 5G is high. On the other hand, the electron injection barrier from ETL6 to EML5B is larger than 0.5 eV, and the light emitting element 10B has lower electron injection efficiency as compared with other light emitting elements 10R / 10G.

As described above, when the CBM of EML5B is shallower than the CBM of EML5R / 5G, the injection of electrons of the light emitting element 10B becomes more difficult than the injection of electrons of other light emitting elements 10R / 10G.

Therefore, in the present embodiment, the injection of holes into EML5B is suppressed by making the layer thickness of IL4B larger than the layer thickness of IL4R / 4G. As a result, in the light emitting device 10B, the carrier balance between the holes and the electrons can be balanced, and the recombination probability between the holes and the electrons can be improved. As a result, the light emitting element 10B can obtain the same brightness as the other light emitting elements 10R / 10G.

As described above, according to the present embodiment, even when the metal chalcogenide is used for HTL3 as described above, the light emitting element 10B and the other light emitting elements 10R / 10G can suppress the same charge. Become. Further, the brightness can be balanced between the light emitting element 10B and the other light emitting elements 10R / 10G.

Further, according to the present embodiment, by making the layer thickness of IL4B larger than the layer thickness of IL4R / 4G, it is possible to achieve the same carrier balance in the light emitting element 10B as in other light emitting elements 10R / 10G. Therefore, according to the present embodiment, it is not necessary to change the material of the ETL6 by the light emitting element 10 to change the CBM of the ETL6, and the ETL6 can be shared.

Further, according to the present embodiment, by providing IL4 as an intermediate layer between HTL3 and EML5 as described above, it is not necessary to consider the hole transport property of IL4, and the light emitting element 10R at the time of manufacture. The hole transportability of 10G and 10B can be easily controlled.

As described above, the IL4R layer thickness and the IL4G layer thickness are preferably 12 nm or less. The layer thickness of IL4B is preferably 0.5 to 12.5 nm.

By setting the layer thickness of IL4B to 0.5 nm or more, IL4B can be formed uniformly, and in-plane variation in hole injection in IL4B can be suppressed. Further, if the layer thickness of IL4 becomes too thick, holes cannot be transported from HTL3 to EML5 by tunneling. By setting the layer thickness of IL4B, which is thicker than IL4R and IL4G, to 12.5 nm or less, hole injection into EML5B by tunneling can be effectively performed even in IL4B.

Further, in the present embodiment, the layer thickness of IL4B in the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength in the light emitting device 100 and the layer thickness of IL4R / 4G in the other light emitting elements 10R / 10G. The difference between them is preferably 0.5 to 12.5 nm.

That is, assuming that the layer thickness of IL4R, the layer thickness of IL4G, and the layer thickness of IL4B are T _ILR , T _ILG , and T _ILB in this order, (T _{ILR +0.5} nm) ≤ T _ILB ≤ (T _ILR + 12.5 nm), Moreover, it is desirable that (T _ILG + 0.5 nm) ≤ T _ILB ≤ (T _{ILG + 12.5 nm).}

By setting the difference in layer thickness between IL4B and IL4R / 4G to 0.5 nm or more in this way, IL4 is formed with a significant difference between the light emitting element 10B and the light emitting elements 10R / 10G other than the light emitting element 10B. Can be filmed. That is, in the above formula, ( _{TILR +0.5} nm) and ( _{TILG +0.5} nm) are uniform films and indicate the minimum values that can be formed with a significant difference. Further, by setting the difference in layer thickness between IL4B and IL4R / 4G to 12.5 nm or less as described above, hole injection by tunneling from HTL3B to EML5B can be effectively performed. That is, in the above formula, (T _ILR + 12.5 nm) and (T _ILG + 12.5 nm) indicate desirable upper limit values at which holes can be effectively tunneled.

As described above, the layer thickness T _ILB of IL4B is larger than the layer thickness T _{ILR of} IL4R and the layer thickness T _{ILG of IL4G.} Therefore, the difference in layer thickness between IL4B and IL4R / 4G indicates T _ILB- T _ILR (where T _ILB > T _ILR ) or T _ILB- T _ILG (where T _ILB > T _ILR ).

Further, as described above, IL4 is _{preferably EA IL} ≤ EA _EML −0.5 eV. Further, it is preferable that IL4 is IP _IL ≧ IP _{EML −0.5 eV.} In other words, if the electron affinity of IL4B is EA _ILB and the ionization potential of _{IL4B is IP ILB} , IL4B is EA _ILB ≤ EA _EMLB -0.5 eV and IP _ILB ≥ IP _EMLB -0.5 eV. preferable. Further, assuming that the electron affinity of IL4R is EA _ILR and the ionization potential of _{IL4R is IP ILR} , IL4R is preferably EA _ILR ≤ EA _EMLR -0.5 eV and IP _ILR ≥ IP _EMLR -0.5 eV. .. Further, assuming that the electron affinity of IL4G is EA _ILG and the ionization potential of _{IL4G is IP ILG} , IL4G is preferably EA _ILG ≤ EA _EMLG -0.5 eV and IP _ILG ≥ IP _EMLG -0.5 eV. ..

The above-mentioned IL4R, 4G, and 4B satisfy all of the above conditions.

Further, as shown in FIG. 2, assuming that the shell thickness of the shell SR is d2, the shell thickness of the shell SG is d12, and the shell thickness of the shell SB is d22, these shell thicknesses d2, d12, and d22 are d22 <d2. And / or d22 <d12 is desirable. That is, the shell thickness d22 of the quantum dots QB in the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength is thinner than the shell thickness d2 / d12 of the quantum dots QR / QG in the other light emitting elements 10R / 10G. Is desirable. As shown in FIG. 2, d2 = d3- (d1 × 2). Similarly, d12 = d13− (d11 × 2) and d22 = d23− (d21 × 2). As described above, the shell thickness d2, d12, and d22 can be easily calculated by subtracting the core diameters d1, d11, and d21 from the outermost particle sizes d3, d13, and d23.

Further, assuming that the ligand length of the ligand LR is d4, the ligand length of the ligand LG is d14, and the ligand length of the ligand LB is d24, these ligand lengths d4, d14, and d24 are d24 <d4 and / or d24 <d14. Is desirable. That is, it is desirable that the ligand length d24 of the quantum dot QB in the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength is shorter than the ligand lengths d4 and d14 in the other

light emitting elements

10R and 10G. The ligand lengths d4, d14, and d24 can be measured by obtaining the distance between the quantum dots QDs adjacent to each other in the same pixel P from the TEM image of the cross section of the EML5R, 5G, and 5B.

Table 3 summarizes the shell thicknesses d2, d12, d22 and ligand lengths d4, d14, d24 of each quantum dot QR, QG, and QB. In Table 3, the values in parentheses indicate suitable ranges for shell thickness d2, d12, d22 and ligand lengths d4, d14, d24. The values in parentheses are specific values of the shell thickness d2, d12, d22 and the ligand length d4, d14, d24 used in the present embodiment, and are the shell thickness d2, d12, d22 and the ligand length d4, d14. -An example of the combination of d24 is shown.

As shown in Table 3, the shell thickness d2 / d12 of the quantum dot QR / QG is preferably 1.5 to 5.0 nm, and the shell thickness d22 of the quantum dot QB is preferably 0.5 to 3.0 nm. Is. The ligand lengths d4 and d14 of the quantum dot QR / QG are preferably 1.5 to 2.5 nm, and the ligand length d24 of the quantum dot QB is preferably 0.5 to 1.5 nm.

It is desirable to increase the distance from the HTL3 to the core of the quantum dot QD in order to prevent the quantum dot QD from being charged and deteriorating the characteristics due to the presence of a hydroxyl group on the surface of the metal chalcogenide in HTL3.

However, as described above, the light emitting element 10B has a lower electron injection efficiency than the

light emitting elements

10R and 10G. Therefore, in the present embodiment, by making the layer thickness T _ILB of IL4B larger than the layer _{thickness T ILR of} IL4R and the layer _{thickness T ILG of} IL4G, hole injection into EML5B is suppressed and carriers in EML5B are suppressed. It's balanced. Therefore, it is difficult for carriers to be injected from IL4 and ETL6 in the quantum dot QB of the light emitting element 10B as compared with the quantum dots QR / QG of other light emitting elements 10R / 10G.

Therefore, as described above, if the shell thickness d22 of the quantum dot QB is made thinner than the shell thickness d2 / d12 of the quantum dot QR / QG, the distance from the IL4B and ETL6 to the core CB of the quantum dot QB can be shortened. it can. As a result, it is possible to inject carriers into the quantum dot QB as effectively as the quantum dot QR / QB, and it is possible to improve the light emission characteristics.

Further, as described above, even when the ligand length d24 of the quantum dot QB is made shorter than the ligand lengths d4 / d14 of the quantum dot QR / QG, the distance from the IL4B and ETL6 to the core CB of the quantum dot QB is also shortened. can do. Therefore, also in this case, it is possible to perform carrier injection equivalent to the quantum dots QR / QB into the quantum dots QB, and it is possible to improve the light emission characteristics.

<Modification example>
In this embodiment, the case where the

light emitting elements

10R, 10G, and 10B are provided with IL4R, 4G, and 4B, respectively, has been described as an example. However, as long as IL4B is provided, IL4R and IL4G do not necessarily have to be provided, _{and at least one of IL4R layer thickness T ILR} and IL4G layer thickness T _ILG is as shown in Table 2. In addition, it may be 0 nm.

That is, in this embodiment, the thickness _{T ILR} of IL4R for a light emitting element 10R, and HTL3R a layer containing a metal chalcogenides, can be words and EML5R, the distance between. Therefore, when the layer thickness T _{ILR of} IL4R is 0 nm, it means that the distance between HTL3R and EML5R is 0 nm, and HTL3R and EML5R are in contact with each other.

Further, the layer thickness T _ILG of IL4G can be rephrased as the distance between HTL3G, which is a layer containing a metal chalcogenide, and EML5G in the light emitting device 10G. Therefore, when the layer thickness T _{ILG of} IL4G is 0 nm, it means that the distance between HTL3G and EML5G is 0 nm, and HTL3G and EML5G are in contact with each other.

Similarly, in the above description, the layer thickness T _ILB of IL4B can be rephrased as the distance between HTL3B, which is a layer containing a metal chalcogenide, and EML5B in the light emitting device 10B.

Therefore, the difference in layer thickness between IL4B and IL4R can be rephrased as the difference between the distance between the HTL3B and EML5B in the light emitting element 10B and the distance between the HTL3R and EML5R in the light emitting element 10R. .. Similarly, the difference in layer thickness between IL4B and IL4G can be rephrased as the difference between the distance between the HTL3B and EML5B in the light emitting element 10B and the distance between the HTL3G and EML5G in the light emitting element 10G. it can.

As described above, in order to suppress the deterioration of the characteristics due to the charging of the quantum dot QD when the metal chalcogenide is used for the HTL3, the distance from the HTL3 to the core of the quantum dot QD may be increased. Therefore, for the quantum dot QR / QG, for example, at least one of the shell thickness d2 / d12 of the quantum dot QR / QG and the ligand length d4 / d14 of the quantum dot QR / QG is in the numerical range shown in Table 3. It may be set to the value in. As a result, unlike the quantum dot QB, it is possible to suppress the deterioration of the characteristics of the quantum dots QR / QG due to charging. Further, as described above, unlike the quantum dot QB, the quantum dot QR / QG has high hole injection efficiency and electron injection efficiency. Therefore, IL4R and IL4G do not necessarily have to be provided.

Further, as described above, in the present embodiment, the case where the layer thickness T _{ILB of} IL4B> the layer thickness T _{ILG of} IL4G = the layer thickness T _ILR of IL4R has been described as an example. However, as described above, the injection of electrons becomes difficult in the order of R → G → B. Therefore, the layer thickness of IL4R / 4G / 4B may be set so that _{the layer thickness of IL4B is T ILB} > the layer thickness of IL4G is T _ILG > the layer thickness of IL4R is T _ILR.

[Embodiment 2]
In this embodiment, the differences from the first embodiment will be described. For convenience of explanation, components having the same functions as the components described in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 6 is a diagram schematically showing an example of a laminated structure of the light emitting device 100 according to the present embodiment.

The light emitting element 10 and the light emitting device 100 according to the present embodiment have the same configuration as the light emitting element 10 and the light emitting device 100 according to the first embodiment, except for the following points.

In the light emitting device 100 according to the present embodiment, a hole injection layer (hereinafter referred to as “HIL”) 11 is provided between the anode 2 and the EML 5 as a layer containing a metal chalcogenide having a hole transporting property. ing. Between HIL11 and EML5, HTL12 containing an organic material is provided as an intermediate layer between HIL11 and EML5. Although HIL11 mainly contains metal chalcogenide, it may also contain other substances. Further, HTL12 mainly contains an organic material, but may also contain other materials.

The light emitting element 10 shown in FIG. 6 includes an anode 2, HIL11, HTL12, IL4, EML5, ETL6, and a cathode 7 in this order from the array substrate 1 side (that is, the lower layer side).

Each of the anode 2, HIL11, HTL12, and EML5 is separated into islands for each pixel P by a bank (not shown).

The light emitting element 10R is formed by island-shaped anodes 2R, HIL11R, HTL12R, EML5R, and common layers ETL6 and cathode 7, respectively. The light emitting element 10G is formed by an island-shaped anode 2G, HIL11G, HTL12G, EML5G, and common layers ETL6 and cathode 7, respectively. The light emitting element 10B is formed by an island-shaped anode 2B, HIL11B, HTL12B, EML5B, and common layers ETL6 and cathode 7, respectively.

However, even in this embodiment, the above configuration is an example, and the configuration of the light emitting device 100 is not necessarily limited to the above configuration. Also in the present embodiment, the light emitting device 100 may include, as the light emitting element 10, a light emitting element that emits light having a light emitting peak wavelength in a wavelength band other than the wavelength band described in the first embodiment. The ETL6 may be separated into islands for each pixel P by the bank. The stacking order from the anode 2 to the cathode 7 may be reversed. Therefore, the light emitting element 10 may include the anode 2, the HIL 11, the HTL 12, the EML 5, the ETL 6, and the cathode 7 in this order from the upper layer side. Hereinafter, a case where the light emitting device 100 has the configuration shown in FIG. 6 will be described as an example.

In the following description, when it is not necessary to distinguish HIL11R / 11G / 11B, these HIL11R / 11G / 11B are collectively referred to as "HIL11". When it is not necessary to distinguish HTL12R / 12G / 12B, these HTL12R / 12G / 12B are collectively referred to as "HTL12".

In this embodiment, the anode 2 injects holes into the HIL 11. HIL11 injects holes into HTL12.

As described above, HIL11 mainly contains metal chalcogenides having hole transporting properties. As the metal chalcogenide, the same material as HTL3 according to the first embodiment can be used. Further, the HIL 11 can be formed by the same method as the HTL 3 according to the first embodiment.

Specific examples of the metal chalcogenide include nickel oxide (eg NiO), copper oxide (e.g., _Cu 2 O), include copper sulfide (e.g., CuS), and the like. Only one kind of these metal chalcogenides may be used, or two or more kinds may be mixed and used as appropriate. Therefore, the metal chalcogenide may be at least one selected from the group consisting of nickel oxide, copper oxide, and copper sulfide.

HIL11 can be formed by, for example, a sol-gel method, a sputtering method, a CVD (chemical vapor deposition) method, a spin coating method (coating method), or the like.

HTL12 transports holes to EML5. The HTL 12 is provided between the HIL 11 and the EML 5 in contact with the HIL 11 and the EML 5.

HTL12 is, for example, poly (N-vinylcarbazole) (abbreviation: PVK), poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (4,4'-(N-4-). sec-butylphenyl)) diphenylamine)] (abbreviation: TFB), which mainly contains organic materials having hole transporting properties. Only one kind of these organic materials may be used, or two or more kinds may be mixed and used as appropriate. Therefore, HTL12 is at least one kind of organic hole transporting material selected from the group consisting of PVK and TFB. It may consist of.

HTL12 can be formed by, for example, a coating method (a method in which the organic hole transporting material is dissolved in a solvent, spin coated, and the solvent is dried), a dip coating method, or the like.

Even in this embodiment, from the viewpoint of versatility of the manufacturing apparatus, it is desirable that the manufacturing apparatus of each layer of the light emitting element 10 is separated from each other. Therefore, it is desirable that the HIL11 manufacturing apparatus and the film forming apparatus used in the next step (that is, the film forming apparatus on the HIL11) are separated from each other. However, when the substrate on which the HIL 11 is formed is conveyed to the manufacturing apparatus separated from the apparatus for producing the HIL 11 after the formation of the HIL 11, the substrate on which the HIL 11 is formed is exposed to the atmosphere between the two manufacturing apparatus.

As described above, from the viewpoint of versatility of the manufacturing apparatus, although the manufacturing process of the light emitting device 100 includes a step of exposing the metal chalcogenide surface of HIL 11 to a gas containing water, each layer of the light emitting element 10 It is desirable that the manufacturing equipment is separated from each other. Then, in the step of exposing the metal chalcogenide surface of HIL11 to a gas containing water, it is assumed that a hydroxyl group is adsorbed on the surface of the metal chalcogenide. Therefore, the fact that the manufacturing process of the light emitting device 100 includes a step of exposing the metal chalcogenide surface of HIL11 to a gas containing water includes a step of adsorbing a hydroxyl group on the surface of the metal chalcogenide. It is presumed to mean that.

HTL12 suppresses the charging of the quantum dot QD by the hydroxyl group on the surface of the metal chalcogenide, and suppresses the deterioration of the light emission characteristic due to the charging of the quantum dot QD.

In the light emitting elements 10R / 10G / 10B according to the present embodiment, the layer thickness of the layers other than HTL12R / 12G / 12B can be set in the same manner as the conventional light emitting element.

Table 4 shows the layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B according to the present embodiment. In Table 4, the layer thickness in parentheses indicates a suitable range of the layer thickness of each layer. The layer thickness outside the parentheses is a specific layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B. Shown.

As shown in Table 4, the layer thickness of HIL11R / 11G / 11B is preferably 5 nm to 50 nm. The layer thickness of HTL12R / 12G is preferably 30 to 59.5 nm. The layer thickness of HTL12B is preferably 30.5 to 60 nm. However, HTL12R / 12G / 12B is set so that the layer thickness of HTL12B> the layer thickness of HTL12R and the layer thickness of HTL12B> the layer thickness of HTL12G.

An example of a method for manufacturing the

light emitting elements

10R, 10G, 10B and the light emitting device 100 according to the present embodiment will be described below with reference to FIGS. 6 and 4.

In the present embodiment, the process until the grid-like bank is formed is the same as that in the first embodiment. Also in the present embodiment, in the same manner as in the first embodiment, an ITO layer having a layer thickness of 100 nm is formed as the

anodes

2R, 2G, and 2B on the array substrate 1, and then a grid-like bank is formed.

In the present embodiment, NiO is then spin-coated on the

anodes

2R, 2G, and 2B, and then heated in the air to form a NiO layer having a layer thickness of 15 nm as HIL11R, 11G, and 11B. HIL formation step).

Next, PVK was dissolved in a solvent, spin-coated, and the solvent was dried to form PVK layers on HIL11R / 11G / 11B as HTL12R / 12G / 12B (HTL forming step). The part other than the film formation target is formed by using a mask, and the layer thickness of HTL12R / 12G / 12B is adjusted by changing the concentration of PVK with respect to the solvent, the rotation speed at the time of spin coating, and the like. went. As a result, a PVK layer having a layer thickness of 40 nm was formed as HTL12B, and a PVK layer having a layer thickness of 30 nm was formed as HTL12R and HTL12G, respectively.

Next, a quantum dot QD layer having a layer thickness of 40 nm was formed on the HTL12R / 12G / 12B as EML5R / 5G / 5B in the same manner as in the first embodiment.

After that, in the same manner as in the first embodiment, the ZnO layer having a layer thickness of 50 nm and the Al layer having a layer thickness of 100 nm made of ZnO-NP are formed in this order, whereby the ETL6 and the cathode 7 common to each pixel P are formed. They were laminated in order. As a result, the

light emitting elements

10R, 10G, and 10B according to the present embodiment were manufactured. Also in this embodiment, the light emitting device 100 is manufactured by sealing the

light emitting elements

10R, 10G, and 10B with a sealing layer (not shown) after the cathode 7 is formed.

7 to 9 are diagrams showing the energy band and layer thickness of each layer in the

light emitting elements

10R, 10G, and 10B according to the present embodiment manufactured in this manner. FIG. 7 shows the energy band and layer thickness of each layer in the light emitting element 10R. FIG. 8 shows the energy band and layer thickness of each layer in the light emitting element 10G. FIG. 9 shows the energy band and layer thickness of each layer in the light emitting element 10B.

As shown in FIGS. 7 to 9, the differences between the light emitting elements 10R / 10G / 10B according to the present embodiment and the light emitting elements 10R / 10G / 10B according to the first embodiment are the anodes 2R / 2G / 2B and the EML5R. Only the layer between 5G and. In this embodiment, as shown in FIGS. 7 to 9, HIL11R / 11G / 11B and HTL12R / 12G / 12B are provided in this order between the anodes 2R / 2G / 2B and the EML5R / 5G. .. The electron affinity of the NiO layer as HIL11R / 11G / 11B (hereinafter referred to as "EA _HIL ") is 1.9 eV, and the ionization potential (hereinafter referred to as "IP _HIL ") is 5.4 eV. _{Further, the electron affinity EA HTL} of the PVK layer as HTL12R / 12G / 12B is 2.2 eV, and the ionization potential IP _HTL is 5.8 eV.

The electron affinity EA _HIL corresponds to the energy difference between the vacuum level (not shown) and the CBM of HIL11R / 11G / 11B. The ionization potential IP _HIL corresponds to the energy difference between the vacuum level and the VBM of HIL11R / 11G / 11B. Further, in the present embodiment, the electron affinity EA _HTL corresponds to the energy difference between the vacuum level (not shown) and the CBM of HTL12R / 12G / 12B. The ionization potential IP _HTL corresponds to the energy difference between the vacuum level and the VBM of HTL12R / 12G / 12B.

In this embodiment, as shown by h + in FIGS. 7 to 9, holes from the

anodes

2R, 2G, and 2B are transferred to EML5R, 5G, and 5B via HIL11R, 11G, and 11B and HTL12R, 12G, and 12B. To reach.

As described in the first embodiment, in the case of the same material system, the conduction band level of the quantum dot QD used as the quantum dot QR / QG / QB becomes deeper as the emission wavelength of the quantum dot QD is longer. , The shorter the emission wavelength of the quantum dot QD, the shallower the energy level.

If the CBM of EML5B is shallower than the CBM of EML5R / 5G, the injection of electrons in the light emitting element 10B becomes more difficult than the injection of electrons in other light emitting elements 10R / 10G.

Therefore, as shown in FIGS. 7 to 9, even in the present embodiment, the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength among the

light emitting elements

10R, 10G, and 10B is another light emitting element 10R. -The electron injection barrier is larger than 10G.

Therefore, in the present embodiment, as described above, the layer thickness of HTL12B is made larger than the layer thickness of HTL12R / 12G. The hole mobility of organic materials is smaller than that of inorganic materials (metal chalcogenides). Therefore, by making the layer thickness of HTL12B larger than the layer thickness of HTL12R / 12G, injection of holes into EML5B can be suppressed. Therefore, also in the present embodiment, in the light emitting device 10B, the carrier balance between the holes and the electrons can be balanced, and the recombination probability between the holes and the electrons can be improved. As a result, the light emitting element 10B can obtain the same brightness as the other light emitting elements 10R / 10G.

As described above, according to the present embodiment, even when the metal chalcogenide is used for HIL11 as described above, the light emitting element 10B and the other light emitting elements 10R / 10G can suppress the same charge. Become. Further, the brightness can be balanced between the light emitting element 10B and the other light emitting elements 10R / 10G.

Further, according to the present embodiment, by making the layer thickness of the HTL 12B larger than the layer thickness of the HTL 12R / 12G, the light emitting element 10B can achieve the same carrier balance as the other light emitting elements 10R / 10G. Therefore, also in this embodiment, it is not necessary to change the material of the ETL6 by the light emitting element 10 to change the CBM of the ETL6, and the ETL6 can be shared.

Further, according to the present embodiment, by providing the HTL 12 as an intermediate layer between the HIL 11 and the EML 5 as described above, it is possible to easily control the layer thickness at the time of manufacturing the HTL 12.

As described above, the layer thickness of HTL12R / 12G is preferably 30 to 59.5 nm. The layer thickness of HTL12B is preferably 30.5 to 60 nm.

A suitable layer thickness of HTL12 is several tens of nm or more, and good hole transportability can be obtained by setting the lower limit of the layer thickness of HTL12R / 12G, which is the lower limit of the layer thickness of HTL12, to 30 nm. it can. Further, in order to suppress an increase in power consumption of the light emitting device 100, the drive voltage is preferably 15 V or less. For example, when the layer thickness of HTL12 is increased by 12 nm, the voltage for obtaining the same brightness is increased by 3 V. Therefore, it is desirable that the upper limit of the layer thickness of HTL12B, which is the upper limit of the layer thickness of HTL12, is 60 nm.

Further, in the present embodiment, the layer thickness of HTL12B in the light emitting element 10B that emits light in the wavelength band having the shortest emission peak wavelength in the light emitting device 100 and the layer thickness of HTL12R / 12G in the other light emitting elements 10R / 10G. The difference between them is preferably 0.5 to 30 nm.

That is, the layer thickness of HTL12R, thickness of HTL12G, the thickness of HTL12B, in _{_{_turn,}} T _{_HTLR,} T _HTLG, _When _{T HTLB, (T HTLR + 0.5nm} ) ≦ T HTLB ≦ (T HTLR + 30nm), and, It is desirable that ( _THTLG + 0.5 nm) ≤ T _HTLB ≤ ( _THTLG + 30 nm).

In this way, by setting the difference in layer thickness between HTL12B and HTL12R / 12G to 0.5 nm or more, HTL12 is formed with a significant difference between the light emitting element 10B and the light emitting elements 10R / 10G other than the light emitting element 10B. Can be filmed. That is, in the above formula, ( _{THTLR +0.5} nm) and ( _{THTLG +0.5} nm) are uniform films and show the minimum values that can be formed with a significant difference. On the other hand, by setting the difference in layer thickness between HTL12B and HTL12R / 12G to 30 nm or less as described above, hole transport from HIL11B to EML5B can be effectively performed. That is, in the above formula, ( _THTLR + 30 nm) and ( _THTLG + 30 nm) indicate desirable upper limit values from which good hole transportability can be obtained.

As described above, the layer thickness _{T HTLB} of HTL12B is greater than the layer thickness _{T HTLG} layer thickness _{T hTLR} and HTL12G of HTL12R. Therefore, the difference in layer thickness between HTL12B and HTL12R / 12G _{indicates THTLB} - _THTLR (however, _THTLB > _THTLR ) or _THTLB - _THTLG (however, _THTLB > _THTLR ).

<Modification example>
As described above, in the present embodiment, the case where the layer thickness THTLB of _HTL12B > the layer thickness THTLG of _HTL12G = the layer thickness _THTLR of HTL12R has been described as an example. However, as described above, the injection of electrons becomes difficult in the order of R → G → B. Therefore, the thickness of HTL12R · 12G · 12B may be set such that the thickness _T HTLB> HTL12G the thickness _T HTLG> HTL12R layer thickness _{T hTLR} of HTL12B.

In the present embodiment, the layer thickness _THTLB of HTL12B can be rephrased as the distance between HIL11B, which is a layer containing a metal chalcogenide, and EML5B in the light emitting device 10B. Further, the layer thickness THTLR of _HTL12R can be rephrased as the distance between HIL11R, which is a layer containing a metal chalcogenide, and EML5R in the light emitting element 10R. Similarly, the layer thickness _THTLG of HTL12G can be rephrased as the distance between HIL11G, which is a layer containing a metal chalcogenide, and EML5G in the light emitting device 10G.

Further, the difference in layer thickness between HTL12B and HTL12R can be rephrased as the difference between the distance between the HIL11B and EML5B in the light emitting element 10B and the distance between the HIL11R and EML5R in the light emitting element 10R. .. Similarly, the difference in layer thickness between HTL12B and HTL12G can be rephrased as the difference between the distance between the HIL11B and EML5B in the light emitting element 10B and the distance between the HIL11G and EML5G in the light emitting element 10G. it can.

The present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

1

Array substrate

2, 2R, 2G,

2B anode

3, 3R, 3G, 3B HTL (layer containing metal chalcogenide, hole transport layer)
4, 4R, 4G, 4B, 4R IL (intermediate layer, insulating layer)
12, 12R, 12G, 12B HTL (intermediate layer, hole transport layer)
5,5R, 5G, 5B EML (light emitting layer)
7

Cathodes

10, 10R, 10G, 10B

Light emitting devices

11, 11R, 11G, 11B HIL (layer containing metal chalcogenide, hole injection layer)
100 light emitting device

Claims

Equipped with a plurality of types of light emitting elements having emission peak wavelengths in different wavelength bands,
The plurality of types of light emitting elements each include an anode, a light emitting layer containing quantum dots, and a cathode in this order, and provide a metal chalcogenide having a hole transporting property between the anode and the light emitting layer. Among the plurality of types of light emitting elements having a layer containing the same, at least in a light emitting element that emits light in the wavelength band having the shortest emission peak wavelength, an organic substance is formed between the layer containing the metal chalcogenide and the light emitting layer. Has an intermediate layer containing the material,
Among the plurality of types of light emitting elements, the distance between the layer containing the metal chalcogenide and the light emitting layer in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is the distance between the other light emitting elements. A light emitting device characterized in that it is larger than the distance between the layer containing the metal chalcogenide and the light emitting layer.
The light emitting device according to claim 1, wherein the intermediate layer is provided between the layer containing the metal chalcogenide and the light emitting layer in all of the plurality of types of light emitting elements.
The light emitting device according to claim 1 or 2, wherein the metal chalcogenide is at least one selected from the group consisting of nickel oxide, copper oxide, and copper sulfide.
The light emitting device according to any one of claims 1 to 3, wherein the intermediate layer is an insulating layer.
In a light emitting device that emits light in the wavelength band having the shortest emission peak wavelength, the distance between the layer containing the metal chalcogenide and the light emitting layer is in the range of 0.5 to 12.5 nm. The light emitting device according to claim 4.
The distance between the layer containing the metal chalcogenide and the light emitting layer in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength, and the layer containing the metal chalcogenide and the above in the other light emitting element. The light emitting device according to claim 4 or 5, wherein the difference from the distance from the light emitting layer is 0.5 to 12.5 nm.
The insulating layer is polymethylmethacrylate, polyvinylpyrrolidone, poly[(9,9-bis (3'-(N, N-dimethylamino) propyl) -2,7-fluorene) -alt-2,7- (9). , 9-Dioctylfluorene)]. The light emitting device according to any one of claims 4 to 6, which comprises at least one kind of insulating material selected from the group.
The light emitting device according to any one of claims 1 to 3, wherein the layer containing the metal chalcogenide is a hole injection layer, and the intermediate layer is a hole transport layer.
A claim characterized in that, in a light emitting element that emits light in the wavelength band having the shortest emission peak wavelength, the distance between the layer containing the metal chalcogenide and the light emitting layer is in the range of 30.5 to 60 nm. Item 8. The light emitting device according to item 8.
The distance between the layer containing the metal chalcogenide and the light emitting layer in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength, and the layer containing the metal chalcogenide and the above in the other light emitting element. The light emitting device according to claim 8 or 9, wherein the difference from the distance from the light emitting layer is 0.5 to 30 nm.
The hole transport layer is poly (N-vinylcarbazole), poly [(9,9-dioctylfluorenyl-2,7-diyl) -co- (4,4'-(N-4-sec-butyl)). The light emitting device according to any one of claims 8 to 10, wherein the light emitting device comprises at least one organic hole transporting material selected from the group consisting of phenyl)) diphenylamine)].
Each of the quantum dots in the plurality of types of light emitting elements includes a core and a shell covering the core.
A claim characterized in that the thickness of the shell of the quantum dots in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is thinner than the thickness of the shell of the quantum dots in the other light emitting elements. Item 2. The light emitting device according to any one of Items 1 to 11.
Each of the light emitting layers of the plurality of types of light emitting elements has a ligand adsorbed on the surface of the quantum dots.
Any of claims 1 to 12, wherein the length of the ligand in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is shorter than the length of the ligand in the other light emitting element. The light emitting device according to item 1.
Each of the plurality of types of light emitting elements includes an electron transport layer between the cathode and the light emitting layer.
The material of the electron transport layer in the light emitting device that emits light in the wavelength band having the shortest emission peak wavelength is the same as the material of the electron transport layer in at least a part of the other light emitting elements. The light emitting device according to any one of claims 1 to 13.
The feature is that the level of the lower end of the conduction band of the light emitting layer in the light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is shallower than the level of the lower end of the conduction band of the light emitting layer in the other light emitting elements. The light emitting device according to any one of claims 1 to 14.
The light emitting element that emits light in the wavelength band having the shortest emission peak wavelength is a light emitting element that emits blue light, and the other light emitting element emits a light emitting element that emits red light and green light. The light emitting device according to any one of claims 1 to 15, wherein the light emitting element is a light emitting element.